<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>Document</title>
</head>

<body>

</body>
<script type="text/javascript">
    var k = 0;
    /*
        var  res = k++ + ++k + k + k++;
        var a = k++;  a = 0  k = 1
        var b = ++k;  b = 2  k = 2
        var c = k;    c = 2  k = 2
        var d = k++;  d = 2  k = 3
        等价于  var res = a +b + c +d

    */
    console.log(k++ + ++k + k + k++) // 结果是多少？为什么？
    console.log(k)
</script>

</html>